Published on October 1st, 2008 | by ziggy20
Reciprocal Roof Frame Building: How-To, Materials, and Supplies
Earlier this year, I was introduced to the concept of a so-called “reciprocal roof frame”. After hearing about the concept from a friend, we later browsed the internet in search of natural buildings featuring this mysterious design. When I finally saw examples of different reciprocal roofs, I was immediately enamored: here was a roof structure so totally simple, strong, and above all, beautiful.
A reciprocal roof is a self-supporting, round structure composed of interlocking beams that equally bear the weight of one another. Composed of as few as three beams, a reciprocal roof can incorporate practically any number of beams and span great distances while still maintaining its integrity. Best suited to round structures, this style of frame is incredibly strong, and “twists upon itself rather than spreading apart”, when pressure is applied from above. Notably, it is an appropriate frame for living roofs, because of its strength. The reciprocal roof is a glorious design for green buildings.
The history of the reciprocal roof seems clouded due to a lack of comprehensive information (a Google search for “reciprocal roof” or related terms will result in only a handful of actual buildings featuring the design, plus some other minimal historical information), but from what I gather, it was designed by Graham Brown in 1987, when the idea came to him from “out of nowhere” (which is also the name of his company).
History aside, the reciprocal roof is also incredibly simple to build, and very appropriate for amateur green builders, and it is perfect for roundhouses and circular structures. It is perhaps most famously featured in the phenomenal low-impact woodland home of Simon Dale (see right), and Tony Wrench’s roundhouse in Wales, two well-known natural buildings in Europe.
How to build a reciprocal roof
There exists an overall dearth of how-to information on the construction of the reciprocal roof, although there is at least one comprehensive resource for aspiring reciprocal roofers. Tony Wrench’s Building a Low-Impact Roundhouse features fairly complete instructions for building a frame, including plenty of photos and sketches to illustrate the process. Other than Earthbag Building by Kaki Hunter and Donald Kiffmeyer, which features a mere paragraph on reciprocal roofs, this is the only published resource. It is a good one and worth tracking down.
My experience building a reciprocal roof frame
Very recently, I had the pleasure of constructing my very own reciprocal roof for a small cob house that I am building (see above). It took two attempts (only because the poles of the first frame were a little lacking, in terms of diameter), but it was a very simple process, and one I would gladly repeat. My own frame is composed of 28 total poles, hand-cut from nearby land, including fourteen primary black locust rafters, and another fourteen secondary rafters that are not tied into the main frame. Eventually, this roof will be covered with an impermeable membrane and become a living roof.
Ultimately, I hope others will learn about and experience the simplicity and beauty of the reciprocal roof frame. It is truly an ingenious design, and perfect for round natural buildings.
Here is an assembly of links that I have found useful in my pursuit of the reciprocal roof:
- Simon Dale’s low impact woodland home has a gorgeous reciprocal roof with gnarly rafters and beautiful slab decking (construction information here)
- Tony Wrench’s website has some photos and information about his living reciprocal roof
- The LessPress Snail Cabin has a reciprocal roof made with dimensional lumber. Also, be sure to check out their Excel spreadsheet for calculating beam lengths and positions for both circular buildings and otherwise
- For math nerds, visit The Pavilion for a very technical description of how reciprocal roofs function
- Zone5 has a brief description with some images of a Tony Wrench-style reciprocal roof construction for a roundhouse here and here
- Check out a scale reciprocal roof model and design using dimensional lumber at Casa de Baro
- Cae Mabon in Snowdonia of North Wales features several buildings with reciprocal roofs. Images here.
- Design Forward has a very brief snippet about the history of the reciprocal roof design